Method of cladding molybdenum



United States Patent Ofilice 3,035,338 Patented May 22, 1082 3,035,338METHOD OF CLADDING MOLYBDENUM Harry E. McCune Ill, Breckenridge, andRemus A. Lula,

Tarentunl, Pa., asslgnors to Allegheny Ludlum Steel Corporation,Brackenridge, Pa., a corporation of Pennsylvania No Drawing. Filed June25, 1958, Ser. No. 744,352

6 Claims. (Cl. 29-4715) This invention relates to an improved method ofcladding molybdenum and particularly to a method of bonding oxidationresistant nickel and iron base cladding alloys to the surface ofmolybdenum and molybdenum base alloys.

Material requirements of military and industrial advancement,particularly in the metals field, are demanding metals and alloys withimproved high temperature properties. An example of such demand is thenecessity to acquire materials with high mechanical properties attemperatures of up to 2000 F. and greater, for uses such as turbineblades for jet aircraft. Molybdenum has been found to be an ideal metalfor such applications from a mechanical standpoint. However, molybdenumis a highly reactive metal, the oxide of which is volatile attemperatures of about 900 F. and higher. The oxide ofmolybdenum formsrapidly at these temperatures. For this reason molybdenum may not beemployed for such high temperature application except where provision ismade to protect the metal against oxidation.

It has long been sought to devise a means to adequately coat molybdenumand alloys of molybdenum with a material that will withstand oxidationat the desired high temperature while permit-ting the molybdenum toprovide the required mechanical properties. It is common practice toemploy corrosion resistant stainless steels or iron base alloys andcorrosion resistant nickel base alloys such as lnconel as cladding formolybdenum. The cladding is generally applied by abrasively cleaning thesurfaces of the contacting metals and then forming a box-like structureby placing the cladding on either side of the molybdenum and weldingside bars around the sides. he boxlike structure is then evacuated ofair and the entire assembly is hot rolled.

Frequently a barrier metal such as chromium plate is applied to themolybdenum core before cladding. This is done to prevent penetration ofnickel and iron into the molybdenum as such alloying ingredients tend tolower the recrystallization temperature of molybdenum. Such a barriermetal, however, does not enhance the bonding qualities of the claddingmetal.

it has now been found that by employing the method of the presentinvention a superior bond may be obtained between the cladding metal andthe molybdenum.

An object of the present invention is, therefore, to provide a cladmolybdenum body that possesses a superior bond between the cladding andthe core.

A further object of the present invention is to purposely provide anoxidized surface to the iron or nickel base cladding metal that isplaced adjacent to the molybdenum before the ciadding operation iscarried out.

Other objects and advantageous features of the present invention relateto the improvement in the bonding of nickel and iron base clad materialsto molybdenum which comprises heating said clad materials in anoxidizing atmosphere in order to obtain an oxidized coating on thesurface of said clad that is placed adjacent to the molybdenum coreprior to hot rolling in order to secure a clad molybdenum structure.

In the practice of the present invention, iron and nickel alloys, and inparticular the stainless steels and nickel base alloys, that possesshigh oxidation resistance at elevated temperatures are purposelyprovided With an oxide scale before being clad to a molybdenum core. Thedesired oxide film provided on the cladding metal is the tenacious darkblue or purple scale type in preference to a loose flaky scale. Such anoxide coating may be obtained by heat treatment in air or any oxidizingatmos phere at nearly any temperature above about 600 F., but preferablyat a temperature not higher than about 2000 F. The reason such a widerange of temperatures is applicable is that a desired tightly adheringoxide film may be secured at the lower temperatures by merely holdingthe material at temperature for longer periods of time. However, forpractical considerations it is desirable to perform this operation in atime of within one hour. Such metal scale or oxide film may be obtainedat the higher temperatures in times as short as one minute. Thepreferred time and temperatures therefore are from about 600 F. to 2000F. for from one hour to one minute, the higher temperatures requiringthe shorter times and the lower temperature requiring the longer times.Optimum results have been obtained on AIS Type 310 stainless steel andInco 702 alloy at temperatures of from about 1600 F. to 1650 F. fortimes of from about five to six minutes. Inco 702 alloy is thedesignation given by the International Nickel Company of New York, NewYork to an alloy of the following approximate analysis: carbon about02%, manganese about 0.10%, iron about 0.35%, nickel about 80.00%,chromium about 15.00%, aluminum about 3.00% and titanium about 0.50%.

The clad surfaces to be bonded need not be abrasively cleaned, butpreferably are cleaned of foreign material such as oils, etc., with asolvent such as trichloroethylene. The oxide coated cladding material isbonded to molybdenum or molybdenum alloy in the conventional manner, thecladding material being placed in sandwich fashion on either side of themolybdenum with the oxide film faced inwardly. Side bars are weldedaround the periphery of the molybdenum in order to form an airtightboxlike construction. A partial vacuum is created in the box before itis heated to a temperature usually of about 2200 F. to be hot rolled tofinish gauge. After hot rolling the side bars are generally sheared offin order to provide the molybdenum clad material.

The general procedure for assembling and hot rolling clad materials isas follows:

(1) The core, cladding and side bars are cleaned.

(2) At least one surface of the cladding is heat treated to provide thedesired oxide film.

(3) The core is placed in the center of one piece of cladding with theoxide film up and the side bars are placed around the core. The otherpiece of cladding is placed on top with the oxide film down. Theassembly is clamped and welded. A space is retained between the sidebars and the cladding for evacuation of air from the assembly. A metaltube is welded into the space to provide a convenient evacuation port.

(4) After welding the assembly is checked for leaks.

(5) The assembly is evacuated at some temperature between roomtemperature and the hot rolling temperature.

(6) After evacuation the evacuation tube is sealed.

(7) The assembly is hot rolled to gauge and stress relieved.

A good vacuum (less than 25 microns) must be obtained before theassembly is sealed. The evacuation. can

be done at any temperature between room temperature and about 2200 F. Atthe higher temperatures the time necessary to obtain the desired vacuumwill result in ex- ..cessive surface oxidation and a poor hot rolledsurface.

At room temperature the metal outgasses very slowly. The evacuation at amoderate temperature, such as 1000 PI, has been satisfactory.

The following specific examples are given to illustrate the presentinvention and in no way limit the invention to the exact procedurefollowed.

Molybdenum alloy plates (Moj.5% Ti), approximately .225 ga. x 1 /2" x 1/2", were clad with Inco 702 alloy and AISI Type 310 stainless steelsheet in both the conventional manner and by the process of the presentinvention. In carrying out the process of the present invention thecladding metal was oxidized at 1600 F. to 1650 F. for five minutes.Oxide scale was cleaned off one side of the cladding metal.

Cladding was carried out essentially as set forth in steps (1) through(7) above, with the exception that in step (2) the clad metal was notoxidized where conventional practice was followed.

The molybdenum alloy plates were cross hatch ground using emery clothbefore cladding. The inside surface of the clad metal employed for theconventional practice was also ground prior to cladding. The side barsemployed were made of nickel, while the assembly was welded with anickel electrode with a single pass all around. Welding was conducted inan argon atmosphere and the assembly was evacuated to create a partialvacuum in the manner described above. A vacuum less than ten microns wasemployed. Hot rolling to a final hot rolled gauge of .050 inch wasaccomplished at a temperature of from about 2100 F. to 2200 F. Thesamples so obtained were then subjected to a peel test. The peel testconsists of peeling a small portion of the cladding on one side awayfrom the core, bending the peeled cladding 180 and peeling the claddingaway from the core with a tensile machine. The values are reported asthe force necessary to separate the cladding from the core for a stripof the rolled product one inch wide. Results are given below in Tables Iand II.

It can be seen in Tables I and II that the oxidized clad materialsprovide a far stronger bond between the cladding and the molybdenum orthe cladding and the barrier metal.

We claim:

1. In the production of a clad molybdenum body wherein a first metalselected from the group consisting of molybdenum and molybdenum basealloys is enclosed in a second metal selected from the group consistingof nickel base alloys and iron base alloys, the space between saidmetals being partially evacuated of air and such structure being hotrolled, the improvement in combination therewith of subjecting thesurface of said second metal that faces said first metal to heattreatment so as to produce a tightly adhering oxide film on said surfaceprior to hot rolling.

2. In the production of a clad molybdenum body wherein a first metalselected from the group consisting of molybdenum and molybdenum basealloys is enclosed in a second metal selected from the group consistingof nickel base alloys and iron base alloys, the space between saidmetals being partially evacuated of air and such structure being hotrolled, the improvement in combination therewith of subjecting thesurface of said second metal that faces said first metal to atemperature of from about 600 F. to about 2000" F. in an oxidizingatmosphere for a time of from one hour to one minute so as to produce atightly adhering oxide film on said surface prior to hot rolling.

3. In the production of a clad molybdenum body wherein a first metalselected from the group consisting of molybdenum and molybdenum basealloys is enclosed in a second metal selected from the group consistingof nickel base alloys and iron base alloys, the space between saidmetals being partially evacuated of air and such structure being hotrolled, the improvement in combination therewith of subjecting thesurface of said second metal that faces said first metal to atemperature of from about 1600 F. to 1650 F. for a time of from five tosix minutes so as to produce a tightly adhering oxide scale on saidsurface prior to hot rolling.

4. In the production of a clad molybdenum body wherein a first metalselected from the group consisting of molybdenum and molybdenum basealloys is sandwiched between two strips of a second metal selected fromthe group consisting of nickel base alloys and iron base alloys, sidebars are welded to the ends and sides to form a box-shaped structure, apartial vacuum is drawn on the interior of said box-shaped structure andsaid box-shaped structure is hot rolled, the improvement in combinationtherewith of subjecting the surface of said second metal that faces saidfirst metal to heat treatment so as to produce a tightly adhering oxidescale on said surface prior to hot rolling.

5 In the production of a clad molybdenum body where in a first metalselected from the group consisting of molybdenum and molybdenum basealloys is sandwiched between two strips of a second metal selected fromthe group consisting of nickel base alloys and iron base alloys, sidebars are welded to the ends and sides to form a box-shaped structure, avacuum of at least 25 microns is drawn on the interior of saidbox-shaped structure and said box-shaped structure is hot rolled, theimprovement in combination therewith of subjecting the surface of saidsecond metal that faces said first metal to a temperature of from about600 F. to about 2000 F. in an oxidizing atmosphere for a time of fromone hour to one minute so as to produce a tightly adhering oxide film onsaid surface prior to hot rolling.

6. In the production of a clad molybdenum body wherein a first metalselected from the group consisting of molybdenum and molybdenum basealloys is sandwiched between two strips of a second metal selected fromthe group consisting of nickel base alloys and iron base alloys, sidebars are welded to the ends and'sides to form a box-shaped structure, avacuum of at least 25 microns is drawn on the interior of saidbox-shaped structure and said box-shaped structure is hot rolled, theimprovement in combination therewith of subjecting the surface of saidsecond metal that faces said first metal to a temperature of from about1600 F. to 1650 F. in an oxidizing atmosphere for a time of from five tosix minutes so as to produce a tightly adhering oxide film on saidsurface prior to hot rolling.

References Cited in the file of this patent UNITED STATES PATENTS1,827,297 Moore Oct. 13, 1931 2,707,821 Sowter May 10, 1955 2,763,057Clair Sept. 18, 1956 2,786,265 Keay Mar. 26, 1957 2,861,327 Bechtold etal. Nov. 25, 1958 2,871,150 Fraser et al. Jan. 27, 1959 2,874,453 Loscoet al. Feb. 24, 1959

1. IN THE PRODUCTION OF A CLAD MOLYBDENUM BODY WHEREIN A FIRST METALSELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM AND MOLYBDENUM BASEALLOYS IS ENCOLSED IN A SECOND METAL SELECTED FROM TH E GROUP CONSISTINGOF NICKEL BASE ALLOYS AND IRON BASE ALLOYS, THE SPACE BETWEEN SAIDMETALS BEING PARTIALLY EVACUATED OF AIR AND SUCH STRUCTURE BEING HOTROLLED, THE IMPROVEMENT IN COMBINATION THEREWITH OF SUBJECTING THESURFACE OF SAID SECOND METAL THAT FACES SAID FIRST METAL TO HEATTREATEMENT SO AS TO PRODUCE A TIGHTLY ADHERING OXIDE FILM ON SAIDSURFACE PRIOR TO HOL ROLLING.